Fluid power piston and cylinder assemblies are very old to actuate conventional working elements. Working element as used is defined as those types of machines or devices conventionally attached or coupled to and driven by a power cylinder or actuator to do major work and include pumps, fluid power presses, power lifts and excavators, for example. Various means and methods have been adopted to control the oscillating stroke of the piston, including reversal and modification of the speed of oscillation, for example. In general, a piston and cylinder assembly are connected to a fluid circuit including the necessary control valves which operate and/or modify the source of fluid power delivered to the cylinder at opposing ends of the piston. Such arrangements can become rather bulky and cumbersome, particularly when the control valve circuitry becomes relatively complex to provide more sophisticated control.
Prior attempts to sense the position of the piston in the cylinder during its path of travel have utilized complex electrical or mechanical switches alone or in combination to generate a signal to the control valve circuitry to reverse the piston stroke. Such arrangements do work, however, they tend to be quite complex and expensive to manufacture and are subject to mechanical failure particularly in applications wherein a high number of cycles is involved.
Prior to the present invention, a satisfactory fluid power sensing and signaling control arrangement, as compared to the prior mechanical or electrical types, has not been developed which accurately and reliably is related to and actuated by the position of the piston in the cylinder during its stroke. Nor has the prior art taught a hydraulic actuator of this type which can be advantageously incorporated into a manifold housing wherein most or all of the fluid circuit connections can be compactly arranged around the cylinder bore which is formed by a central bore in the manifold housing, which housing also serves as a convenient mounting surface for various control valves.